What does a tachometer measure?

A tachometer is an instrument specifically designed to measure the rotational speed of an object, typically an engine’s crankshaft or a motor shaft, which is expressed in revolutions per minute (RPM). This measurement is crucial for various automotive and mechanical applications as it allows operators to monitor engine performance, ensuring that the engine operates within optimal RPM ranges for efficiency and to prevent mechanical failure.

Understanding the rotational speed is important because it directly relates to energy output and can affect torque and power delivery, which are vital for efficient operation. By monitoring the RPM, drivers can make necessary adjustments in driving habits, shifting gears at appropriate intervals to maintain performance and fuel economy. The context for this measurement is fundamental in automotive engineering, as excessive RPM can lead to engine damage, while too low an RPM may indicate insufficient performance.

Since the other options deal with different measurements—like distance traveled, engine torque, and engine temperature—they do not pertain to what a tachometer is specifically designed to measure.